Sound-reproducing apparatus



Nov. ll, 1930. H. c. BRADsHAw Er ,AL 1,780,899

SOUND REPRODUCING APPARATUS Filed Deo. .'5. .1927

4 v ayOam/fy Patented Nov. 11, 1930` UNITED STATES PATENT ori-'ica HAROLD C. IBRADSHAW AND MATTHEW J'. DE FOREST, OF CHICAGO, ILLINOIS, AS-

SIGNORS, BY MESNE ASSIGNMENTS, TO UNITED RESEARCH CORPORATION, OF ISLAND CITY, NEW YORK, A CORPORATION OF DELAWARE LONG SOUND-REPRODUCING APPARATUS Application led December 3, 1927. SerialNo. 237,555.

Our invention relates to devices for converting electrical currents into sound vibrations andvmore particularly to couplings for connecting a plurality of loud speakers to a thermionic amplifier.

One object of our invention is to provide a device for coupling an additional loud speaker to an amplifier which is coupled by a transformer to a loud speaker designed for use with said amplifier.

Another object of our invention is to provide a device of the type mentioned which is of such nature that the connection to either of said loud speakers' kmay be interrupted without impairing the' satisfactory operation of the other loud speaker.

A further object of our invention is to 'provide switch controlled devices for connecting a plurality of additional loud speakersto an amplifier which is coupled by a transformer to a loud speaker designed for use with the amplifier, the switch controlled devices being operable to permit the separate or simultaneous use of the additional loud speakers, or to open one or more circuits, and thereby render one or more of the additional loud speakers inoperative.

Other objects and advantages will appear as the description proceeds.

The accompanying drawing is a diagrammatic view of an apparatus embodying our invention.

1 designates the final electron tube of an amplifyin device such as a radioreceiving set, the tue having the usual plate 2, a filament 3 and a grid 4, the connections of the filament grid not being shown as they are well known. From the plate 2, a conductor 5 extends to the primary coil 6 on -a transformer 7, the secondary coil 8, of which is connected to a loud speaker 10, theconnections including a switch 11.

The primary coil 6 is also connected to the positive terminal of a source of potential 12. A conductor 13 extends from the negative terminal of the source of potential to an ,intermediate point on a conductor 14 which is connected at one end to a terminal of a loudv speaker 15 and at the other end is in contact with a switch 16 in the o' position of the latter. The switch is connected by means of a conductor 17 to the other terminal of the loud speaker 15. A conductor 18 extends tion of the latter to the switch 16, with which it makes contact in the on latter. c

The switch 22 controls the operation of the position of the loud speaker 20. When this switch is in its on position and the switch 16 is in off position, the current travels through the conductor 5, the conductor 23, including condenser v24, the switch 22 and the conductor 21, energlzes the loud speaker 20, and continues through the conductors 18 and 17, the switch 16 and t-he conductors 14 and 13. .Under these conditions it will be apparent that the loud speaker 20 is operative while the loud .speaker 15l is inoperative.

'To operate the loud speaker 15 and render the loud speaker 20 inoperative, vthe switch 22 is moved to oit position, and the switch 16 is m'oved to on position. The current then traverses conductors 5 and 23, the switch 22, the conductor 25, the switch 16 and the conductor 17; energizes the loud speaker 15 and continues through the conductors 14 and 13.

To operate loud speakers 15 and 2O simultaneously, both the switches 16 and 22 are moved to on 'position and the current then traverses conductors 5 and 23, switch 22, conductor 21, loud speaker 20, conductor 18, loud speaker 15 and conductors 14 and 13.

When both of the switches 16 and 22 are in o' positions, neither of the loud speakers 15 and 20 is operative, as will be obvious, and no current traverses conductor 23 or 13.

By meansof the switch 11, the operation of the loud speaker 10 is controlled and it may be operated alone or simultaneously with either or both of the loud speakers 15 or 20.

In a model in which the invention has been within the scope of the appended claims.

actually embodied, the loud speaker 10 was of the low impedance type, while 'the loud speakers 15 and 20 were of the high impedance type. The primary and secondary impedance of the output transformer were matched with the plate im edance and the impedance of the loud spea er 10. Because of the use of the condenser 24, currents of audio frequency are by-passed, but the satisfactory operation of the loud speaker 10 was not disturbed by the use or non-use of either or both of the loud speakers 15 and 20. By arranging the condenser 24 in series with both of loud speakers 15 and 20 the impedance of the load on the tube 1 was prevented from decreasing to a point that would impair thel quality of reproduction in any of the loudspeakers.

The importance of the invention will be vapparent when it is considered that'it makes possible the couplin of additional` loud s eakers to an am li er cou led by'a'trans- P lla) is designed for former to a repro ucenwhic usewitlrthe am lifie fwith{..nQ-,fhappreciable distortionY regar less" l.Wliichjspeaker or combination of speakers" is functioning.

Our invention is no1'I limited tothe specific details of the constructions illustrated and described, but diverse. modifications may be made within the spirit thereof. For instance, still other loud speakers may be added by employing the principles described. A substantial range of equivalents is contemplated What we claim and desire to protect by Letters Patent is:

1. The combination of a thermionic amplifier for amplifying audio frequency currents, a loud speaker, a transformer coupling said loud speaker to said amplifier and a second loud speaker connected to said amplifier at a point between said amplifier and said transformer.

2. The combination of a thermionic amplier for amplifying audio frequency currents, a loud speaker, a transformer coupling said Aloud speaker to said amplier, and a plurality ofv additional loud speakers connected to said amplifier at a point between said amplifier and said transformer.

3. The combination of a thermionic amplifier for amplifying audio frequency currents, a loud speaker, a transformer having a secondary lcoil connected to said loud speaker and a primary coil connected to said amplifier, and a condenser and a loud speaker connected in series with each other and connected to said amplier in parallel with said pri-v mary coil.

4. The combination of a thermionic amplifier for amplifying audio frequency currents,

a loud speaker, a transformer having a secondary coil connected to said loud speaker and aV primary coil connected to said amplifier, acondenser and a plurality of additional loud speakers, said condenser and said additional loud speakers being connected in series with each other and connected to said amplifier in parallel with said primary coil.

5. The combination of a thermionic amplifier for amplifying audio frequency currents and having an out-put conductor, a loud speaker, a transformer having a secondary coil connected to said loud speaker, and a primary coil connected to said conductor, a 'source of potential connected in series with said primary coil, and a condenser and a second loud speaker connected in series with each other and in parallel with said primary coil and said source of potential.

6. The combination of a tliermionic amplifier for amplifying audio frequency currents, a loud speaker, a transformer coupling said loud speaker to said amplifier, a ysecond loud l ondary coil connected to said loud speakers` and a primary coil connected toksaid amplifier, a plurality of additional'loud speakers connected to said amplifier in series with each other and in parallel with saidprimary coil, and a switch in the connections of said plurality of loud speakers which in open position renders them inoperative.

8. The combination of a thermionic amplifier for amplifying audio frequency currents, a loud speaker, a transformer having a primary coil and a secondary coil,sa'id primary coil being connected to said amplifier, a second loud speaker, and means for completing a circuit selectively either between said secondary coil and the first mentioned loud speaker, or between said second loud speaker and 'said amplifier, or simultaneously between said secondary coil and the said first mentioned loud :speaker and between said second loud speaker and said amplifier. y

9. The' combination of a thermionic amplifier for amplifying-audio frequency currents,

tion renders said second loud speaker inop-v a loud speaker', a transformer, including a v secondary coil connected to said loud speaker and a primary coil connected to said amplifier, and a second loud speaker and a condenser connected to said amplifier in series with each other and in parallel with said primary coil, and a switch in the connection for said condenser and said second loud speaker, which in open position renders said second loud speaker inoperative.

11. The combination of a thermionic amplifier for amplifying audio frequency currents, having an out-put conductor,a loud speaker, a transformer having a secondary coil connected to said loud speaker and a primary coil connected to said conductor, a source of potentialconnected in series with said primary coil, and a,condenser, a .second loud speaker, and a switch connected in series with each other and in parallel with said primary coil and said source of potential, said second loud speaker being inoperative when said switch is in open position.

l2. The combination of a thermionic ampliier for amplifying audio frequency currents, a loud speaker, a transformer having a secondary coil connected to said loud speaker and a primary coil connected to said amplifier, a pair'of additional loud speakers, a switch for each of said additional loud speakers, and means operable when either of said switches is in on position and the otheris in off -position for completing a circuit from said amplifier through the loud speaker corresponding to the switch in on position, said.' other additional loud speaker remaining inoperative.

13. The combination of a thermionic amplifier for amplifying audio frequency currents,- a loud speaker, a transformer having a secondary coil connected to said loud speaker and a primary coil connected to said amplifier, a pair of additional loud speakers, a switch for each of said additional loud speakers, and means operablel when onel of said switches is in on position,and the other common terminal and each having an opposite individual terminal, of means for effecting energization of said devices either selectivel or simultaneously, comprising two `single-po e, double-throw switches, one of said switches being arranged to connect one side of the circuit either to the vindividualterminal of one'of said devices or to one terminal of the other of said switches, and the latter switch being arranged to connect said common terminal of said devices either,

to said one terminal of said latter switch or to the individual terminal of the other of said devices.

16. In an electric circuit, the combination with two electro-responsive devices having of the switches to the individual terminal of one of said devices, a connection from theother terminal of said one of saidswitches toone terminal off the other of said switches, a connection from the common terminal of said devices to the contacting member of said other of the switches, and connections from the other terminal of said other of said switches to the individual terminal of the other of said devices and to the other side of the circuit.

HAROLD C. BRADSHAW. MATTHEW J. DE FOREST.

is in 0H position for completing a circuit from` l said amplifier through the loud speaker corresponding to the switch in on position, said Y other additional loud speaker remaining inoperative both of said switches being movable to off position to render said additional loud speakers simultaneously inoperative.'

14. In an electric circuit, the combination with a plurality of electro-responsive devices, of means for effecting energization of said devices either selectively or simultaneously, comprising a plurality of single-pole, doublethrow switches, one of said switches being' arranged to connect one side of the circuit either to one termlnal of one of said devices or to one terminal of another of sald switches,

and said other of said switches being arrangedI to connect the other terminal of said one of said devices and one terminal of another of said devices either to said one terminal of said other switch or to the other terminal of said other of said devices.

15. In an electric circuit, the combination with two electro-responsive devices having a 

